Ring oscillators are widely used in high speed circuit applications, and usually include simple inverting logic circuits as stages. For example, each stage includes an N-channel transistor and a P-channel transistor. The stages are connected in series to form a cascade loop. The current output of each stage charges or discharges an input capacitance of a next stage to a threshold voltage. At a particular frequency, a certain phase shift (e.g., 180°) is imparted to signals passing around the loop. If the loop gain is large enough, the signals may become non-linear resulting in square-wave oscillations which can be used, for example, for signal processing.